This invention generally relates to apparatus and methods for controlling temperature of portions of a turbine engine and more particularly, to apparatus for and a method of cooling a seal housing of a bearing compartment of such an engine.
In the construction of turbine engines, there is a need to provide robust shaft bearing systems that can tolerate operation in adverse environmental conditions. Typically, these bearing systems are exposed to high temperature environments that develop from heat produced by operation of the engine.
Turbine engines run at high rotational speeds. A lubricating fluid circulation system is employed to maintain a proper operating environment for bearings that support shafts of such engines. This fluid circulation technique mandates that bearings are housed in a sealed bearing compartment. Shaft exit regions of such bearing compartments are subject to heat buildup with a potential for deleterious coking of lubricating oil.
This re-circulating oil has an obvious beneficial effect of providing lubrication for the bearings. But, there is also a cooling function that is performed by the re-circulating oil. This cooling function prevents deterioration of the bearings which would otherwise occur at high temperatures.
In a typical aircraft turbine engine, lubricating oil is circulated through a bearing compartment at rates that exceed a gallon per minute. The oil must be pressurized in order to achieve the desired re-circulation.
In order to prevent escape of the pressurized oil from the bearing compartment, the compartment must be sealed at points where a rotating shaft passes through the compartment. It is common practice to employ a carbon-ring shaft seal to perform this sealing function. While carbon-ring shaft seals are quite effective for this sealing function, they suffer from a temperature build-up problem. Frictional interaction between the carbon-ring seal and the shaft produces localized heat. That heat, if left uncontrolled, produces coking of the lubricating oil in the region near the seal. Coking cannot be tolerated in an engine that must operate reliably for long periods of time.
This coking is a well-recognized phenomenon which has been addressed in the prior art by directing the re-circulating oil to the region where frictional heat is produced. Typically, the re-circulating oil is sprayed onto the seal-shaft interface to produce localized cooling of that region.
In some instances, additional mechanisms are used to propel fluid into a seal-shaft interface region. For example, US Application Publication 2004/0179935 A1 describes a shaft seal configuration in which a fluid jet propels fluid towards a carbon-ring seal. The fluid gathers in a weir pool and is distributed from the pool by scatter deflection and controlled leakage from the weir pool into the shaft-seal interface.
In other instances, seal supports are provided with fluid passageways that allow fluid to be pumped onto contacting surfaces of a seal. This technique is illustrated in U.S. Pat. No. 5,622,438.
These prior art approaches to heat control have some counterproductive effects. As oil is driven directly at the interface, an increased risk of oil loss develops. When a portion of the oil is diverted to flow to the seal, there is an increase in turbulence and churning. Such churning diminishes the effectiveness of the oil as a lubricant.
As can be seen, there is a need for a bearing system that reduces deleterious effects of oil loss and oil churning encountered in the prior art. More particularly, there is a need for a structure and method that provides for fluid cooling of a seal housing without directing unconstrained lubricating oil onto a shaft-seal interface.